Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session L13: Focus Session: Nanostructured LaAlO3/SrTiO3 Heterostructures |
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Sponsoring Units: DMP Chair: Jeremy Levy, University of Pittsburgh Room: 007D |
Wednesday, March 4, 2015 8:00AM - 8:12AM |
L13.00001: Ultrafast Optical Response of Graphene/LaAlO$_3$/SrTiO$_3$ Nanostructures Lu Chen, Giriraj Jnawali, Mengchen Huang, Jen-Feng Hsu, Feng Bi, Hyungwoo Lee, Sangwoo Ryu, Chang-Beom Eom, Brian D'Urso, Patrick Irvin, Jeremy Levy The exceptional electronic and optical properties of graphene make it promising for tunable plasmonic device applications in the terahertz regime. Plasmons can be induced in graphene by femtosecond laser excitation and its resonance frequency can be tuned over a broad terahertz range by varying the graphene pattern size or gate voltage.\footnote{L. Ju, \textit{et al.}, Nature Nanotech. \textbf{6}, 630 (2011)} Recently, generation, and detection of broadband terahertz (around 10 THz) radiation from 10-nm-scale LaAlO$_3$/SrTiO$_3$ nanostructures created by conductive atomic force microscope (c-AFM) lithography has been demonstrated.\footnote{Y. Ma, \textit{et al.}, Nano Lett. \textbf{13}, 2884 (2013)} This unprecedented control of THz radiation at 10 nm length scales creates a pathway toward hybrid THz functionality in graphene/LaAlO$_3$/SrTiO$_3$ nanostructures. We will discuss efforts to probe graphene plasmonics and its tunability by using this nanoscale THz spectrometer. [Preview Abstract] |
Wednesday, March 4, 2015 8:12AM - 8:24AM |
L13.00002: Probing the nanoelectromechanical properties of LaAlO$_3$/SrTiO$_3$ SketchSETs A. Gauthier, F. Bi, H. Lee, S. Ryu, C. B. Eom, P. Irvin, J. Levy The LaAlO$_3$/SrTiO$_3$ (LAO/STO) interface exhibits a locally-tunable metal-insulator transition. This property can be applied to create nanoscale electronic devices such as sketched single-electron transistors (SketchSETs) at the LAO/STO interface. A SketchSET consists of a quantum dot coupled to source, drain, and gate electrodes. LAO/STO possesses a coupling between lattice distortion and carrier density; mechanical strain applied to the surface can tune the conductance at the interface. Leveraging this property may allow for strain-based control over the electron occupancy of a SketchSET. We use a cryogenic scanning probe microscope to create (at room temperature) and measure (at low temperature) the electronic properties of SketchSET devices and probe their unique nanoelectromechanical properties. [Preview Abstract] |
Wednesday, March 4, 2015 8:24AM - 8:36AM |
L13.00003: CVD-grown graphene on LaAlO$_3$/SrTiO$_3$: transferring, patterning and c-AFM lithography Mengchen Huang, Giriraj Jnawali, Jen-Feng Hsu, Hyungwoo Lee, Sangwoo Ryu, Feng Bi, Lu Chen, Fereshte Ghahari, Jayakanth Ravichandran, Philip Kim, Chang-Beom Eom, Brian D'Urso, Patrick Irvin, Jeremy Levy Interesting properties are anticipated when graphene is integrated with complex-oxide heterostructures. To create these structures, single-layer graphene is grown by chemical vapor deposition and transferred onto LaAlO$_3$/SrTiO$_3$. following a deep UV exposure method, the size and position of the graphene can be patterned to be compatible with the c-AFM lithography technique applied on LaAlO$_3$/SrTiO$_3$. Local control of metal-insulator transition at LaAlO$_3$/SrTiO$_3$ interface is reversibly achieved using the c-AFM lithography technique without observable graphene degradation. The graphene layer can also serve as a top gate to modulate the LaAlO$_3$/SrTiO$_3$ interface conductance. [Preview Abstract] |
Wednesday, March 4, 2015 8:36AM - 9:12AM |
L13.00004: High-energy photoemission studies of oxide interfaces Invited Speaker: Ralph Claessen The interfaces of complex oxide heterostructures can host novel quantum phases not existing in the bulk of the constituents, with the high-mobility 2D electron system (2DES) in LaAlO$_{3}$/SrTiO$_{3}$ (LAO/STO) representing a prominent example. Despite extensive research the origin of the 2DES and its unusual properties -- including the supposed coexistence of superconductivity and ferromagnetism -- are still a matter of intense debate. Photoelectron spectroscopy, recently extended into the soft (SX-ARPES) and hard (HAXPES) X-ray regime, is a powerful method to provide detailed insight into the electronic structure of these heterostructures and, in particular, of the buried interface. This includes the identification of the orbital character of the 2DES as well as the determination of vital band structure information, such as band alignment, band bending, and even k-resolved band dispersions and Fermi surface topology. Moreover, resonant photoemission at the Ti L-edge reveals the existence of two different species of Ti 3d states, localized and itinerant, which can be distinguished and identified by their different resonance behavior. The role of oxygen vacancies is studied by controlled \textit{in-situ} oxidation, which allows us to vary the composition from fully stoichiometric to strongly O-deficient. By comparison to free STO surfaces we can thus demonstrate that the metallicity of the heteointerfaces is intrinsic, $i.e.$ it persists even in the absence of O defects. I will discuss our photoemission results on LAO/STO heterostructures in both (100) and (111) orientation as well as on the related system $\gamma $-Al$_{2}$O$_{3}$/STO(100), which also hosts a 2DES with an even higher mobility. Work in collaboration with J. Mannhart (MPI-FKF, Stuttgart), N. Pryds (TU Denmark), G. Rijnders (U Twente), S. Suga (U Osaka), M. Giorgoi (BESSY, HZB), W. Drube (DESY Photon Science), V.N. Strocov (Swiss Light Source), J. Denlinger (Advanced Light Source, LBNL), and T.-L. Lee (Diamond Light Source). [Preview Abstract] |
Wednesday, March 4, 2015 9:12AM - 9:24AM |
L13.00005: Probing simulated 1D quantum materials using single quantum channels Megan Kirkendall, Patrick Irvin, Jeremy Levy, Hyungwoo Lee, Sangwoo Ryu, Chang Beom Eom Quantum simulation of strongly correlated electronic systems remains an important long-range goal in the field of quantum information. Thus far, much progress has been made with ultracold atomic simulators which can resolve individual atoms and a variety of interesting phases. Nanoscale control of the metal-insulator transition at the LaAlO$_3$/SrTiO$_3$ interface\footnote{Cen, C. \textit{et al.} Nature Mater. \textbf{7}, 298--302 (2008).}, combined with the wide variety of phenomena this system exhibits such as superconductivity and magnetism, provides an alternate approach to solid-state quantum simulation. Our research currently focuses on measuring the properties of 1D simulated materials at the LaAlO$_3$/SrTiO$_3$ interface, at high magnetic fields, using quantum point contacts as well-defined probes. [Preview Abstract] |
Wednesday, March 4, 2015 9:24AM - 9:36AM |
L13.00006: Investigating dimensional crossover of spin-orbit coupling in LaAlO$_3$/SrTiO$_3$ nanowires Rongpu Zhou, Michelle Tomczyk, Guanglei Cheng, Shicheng Lu, Mengchen Huang, Patrick Irvin, Hyungwoo Lee, Sangwoo Ryu, Chang-Beom Eom, Jeremy Levy Weak anti-localization is a macroscopic observation of a quantum transport phenomenon in two-dimensional systems with spin-orbit coupling in which destructive self-interference of carrier trajectories leads to an enhanced conductivity at low magnetic fields. Characterizing spin-orbit coupling at the LaAlO$_3$/SrTiO$_3$ (LAO/STO) interface is important in realizing this system's potential as a principal host for oxide nanoelectronics. Previously, the spin-orbit coupling at the 2D LAO/STO interface was shown to be gate-tunable. Here, we study a crossover from 2D to 1D regimes using nanowires at the LAO/STO interface using weak anti-localization measurements. Transport measurements were performed on nanowires with widths varying from 200 nm down to 10 nm. A series of magnetoresistance measurements were performed at various backgate voltages to study carrier-density dependence. The results are fit to both 2D and 1D models of a weak anti-localization conductance correction due to Rashba spin-orbit coupling.\footnote{Y. Kim, et al., Phys. Rev. B 87, 245121 (2013).} [Preview Abstract] |
Wednesday, March 4, 2015 9:36AM - 9:48AM |
L13.00007: Quantized conductance through quantum point contacts in LaAlO$_3$/SrTiO$_3$ nanowires Anil Annadi, Shicheng Lu, Guanglei Cheng, Michelle Tomczyk, Mengchen Huang, Hyungwoo Lee, Sangwoo Ryu, Chang-Beom Eom, Patrick Irvin, Jeremy Levy Abstract: Scaling of electronic device density is key for any material system to be considered as potential for electronics, which demands ballistic devices at the nanoscale. Here we present the investigation of ballistic transport in LaAlO$_3$/SrTiO$_3$ nanowire devices that act as quantum point contacts. In these devices, electron transport shows quantized conductance up to 3rd sub-band energy levels. We also observe odd integer conductance in the units of $e^2/h$ at high magnetic fields, further indicating spin-resolved quantum transport. We analyze the strength of the Zeeman spin-splitting for various sub-bands induced by magnetic field, where 1D sub-bands show a linear Zeeman splitting for out of plane magnetic field. From the transconductance and magnetic field dependence measurements we extract a g-factor for each of these sub-bands. We discuss the various factors related to spin-resolved transport in these devices. Acknowledgements: We gratefully acknowledge financial support from the following agencies and grants: AFOSR (FA9550-10-1-0524 and FA9550-12-1-0268), NSF (DMR-1124131 and DMR-1104191), AFOSR FA9550-12-1-0342 (CBE)), and DMR-1234096 (CBE). [Preview Abstract] |
Wednesday, March 4, 2015 9:48AM - 10:00AM |
L13.00008: Analysis of local conductance switching by AFM-writing at the LaAlO$_{3}$/SrTiO$_{3}$ interface Margherita Boselli, Danfeng Li, Wei Liu, Alexandre F\^ete, Stefano Gariglio, Jean-Marc Triscone A two dimensional electron liquid is present at the interface between LaAlO$_{3}$ and SrTiO$_{3}$; this system exhibits several interesting physical properties, including tunable superconductivity. In heterostructures with 3 unit cells of LaAlO$_{3}$, an insulator to metal transition can be induced by the electric field effect. We report here on the use of the atomic force microscopy writing technique developed in the group of J. Levy [1] to locally switch on and off conductivity at the interface. Our results show that a quarz resonator AFM sensor is particularly suitable for this purpose. In this configuration, the measurements can be performed in the dark, strongly reducing photo-doping. Electronic nanostructures are found to be particularly sensitive to the writing procedure and to the ambient humidity. We discuss how these parameters can be optimized to confine electrons in regions down to tens of nanometers. Simulations of the conductance changes upon AFM writing are compared to experiments. The temperature evolution of the conductance shows that nanowires are metallic.\\[4pt] [1] C. Cen, et al., Nat Mater 7, 298 (2008) [Preview Abstract] |
Wednesday, March 4, 2015 10:00AM - 10:12AM |
L13.00009: Anisotropic superconducting properties of nanowires at the LaAlO$_3$/SrTiO$_3$ (110) interface Patrick Irvin, Mengcheng Huang, Anil Annadi, Guanglei Cheng, Jeremy Levy, Kalon Gopinadhan, Thirumalai Venkatesan, Ariando Ariando The superconducting properties of nanowires created on anisotropic SrTiO$_3$ (110) surfaces were investigated. Nanowires are created using conductive AFM (c-AFM) lithography at the LaAlO$_3$/SrTiO$_3$(110) interface along the (001) and (1$\bar{1}$0) crystallographic directions. In these devices we observe anisotropic superconductivity. The upper critical magnetic field along the (001) and (1$\bar{1}$0) directions are found to be markedly different with a superconducting dome that is shifted for the two orientations. These observations can be explained by anisotropic orbital binding of Ti and O atoms or the differences in the spin-orbit coupling along the two different directions. [Preview Abstract] |
Wednesday, March 4, 2015 10:12AM - 10:24AM |
L13.00010: One-dimensional Quantum Wire Formed at the Boundary Between Two Insulating LaAlO3/SrTiO3 Interfaces Alon Ron, Yoram Dagan We grow a tiled structure of insulating two dimensional LaAlO3/SrTiO3 interfaces composed of alternating one and three LaAlO3 unit cells. The boundary between two tiles is conducting. At low temperatures this conductance exhibits quantized steps as a function of gate voltage indicative of a one dimensional channel. The step size of half the quantum of conductance is an evidence for absence of spin degeneracy. [Preview Abstract] |
Wednesday, March 4, 2015 10:24AM - 10:36AM |
L13.00011: Metal-insulator transition in nanostructured SrTiO$_3$/LaAlO$_3$ Houlong Zhuang, Valentino R. Cooper, P. Ganesh, Haixuan Xu, P. R. C. Kent It is well known that an insulator-to-metal transition occurs at SrTiO$_3$/LaAlO$_3$ epitaxial heterostructures when the number of LaAlO$_3$ layers reaches a critical value of four. With first-principles calculations, we show that instead of requiring the threshold number of layers to trigger metallicity, the so-called 1+2 overlayer heterostructure also exhibits metallic states. Interestingly, we demonstrate that these metallic states form a two-dimensional electron gas at the overlayer heterostructure. We understand that these fascinating phenomena originate from a modified ``polar catastrophe" model, where the overlayer heterostructure accumulates an electrostatic potential more rapidly than regular heterostructures, leading to the reduction of number of LAO layers. Using this model, we further show that the thinner 1+1 overlayer heterostructure exhibits a similar 2DEG. Our work provides a novel approach of inducing 2DEGs in oxide heterostructures, which are beneficial for modern electronics applications. [Preview Abstract] |
Wednesday, March 4, 2015 10:36AM - 10:48AM |
L13.00012: Nanoscale Electrostatic Confinement at Oxide Interfaces Srijit Goswami, Emre Mulazimoglu, Lieven Vandersypen, Andrea Caviglia We develop a robust and versatile platform to define nanostructures at oxide interfaces via patterned top gates. Using LaAlO$_3$/SrTiO$_3$ as a model system, we demonstrate controllable confinement of electrons to nanoscale regions in the conducting interface. The excellent gate response, ultra-low leakage currents, and long term stability of these gates allows us to perform a detailed study of devices in a split-gate geometry. Electrical transport through such devices displays a distinct threshold associated with depletion directly below the gates, resulting in the formation of a narrow conducting channel even at room temperature. We examine the effects of cross-talk between the gates, and also show that a combination of top gates and back gate can be used to efficiently modulate charge transport through these nanostructures. [Preview Abstract] |
Wednesday, March 4, 2015 10:48AM - 11:00AM |
L13.00013: Lateral probing of the LaAlO3/SrTiO3 two-dimensional electron liquid M.P. Stehno, A.E.M. Smink, H. Hilgenkamp, A. Brinkman The 2-dimensional electron liquid (2DEL) at the interface between the insulating oxides lanthanum aluminate and strontium titanate (LAO/STO) has a complex band structure and hosts novel electronic phases with magnetism and superconductivity. Electrical characterization of the 2DEL has focused mainly on magnetotransport in films or confined geometries, and on z-axis tunneling. We contacted the LAO/STO interface laterally and obtained a gate-tunable barrier between the 2DEL and the metallic electrode. Features in the differential conductance spectra are spaced by energies similar to the confinement energy at the oxide interface and may thus yield information on the (sub-) band structure of 2DEL and barrier region. [Preview Abstract] |
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